Overvoltage protector for high or medium voltage

ABSTRACT

An overvoltage arrester for high or medium voltage is described which includes an arrester block arranged inside a sealed, gas-tight enclosure housing, a sensor, in 5 particular a temperature sensor in the form of a surface wave sensor, is arranged inside the enclosure housing. The surface wave sensor is arranged in a housing that is designed as an antenna.

FIELD OF THE INVENTION

The present invention relates to an overvoltage arrester for high ormedium voltage having an arrester block arranged inside a sealed,gas-tight enclosure housing.

BACKGROUND INFORMATION

An overvoltage arrester of this kind is described in heretofore, e.g.,A2 European Patent Application No. 0 388 779 A2.

When an arrester having no spark gap is in its standby state, leakagecurrent flows through the non-linear resistor elements, causing the bodyof the arrester to heat up slightly. As the arrester gets older, thisleakage current may slowly increase, thus raising the averagetemperature of the arrester.

By measuring the temperature increase in the arrester having no sparkgap, one can monitor the extent to which it has aged. Moreover, inarresters having a spark gap, by measuring the temperature one can drawcertain conclusions about processes in the arrester. In addition, it isuseful to obtain information about further operating variables of thearrester, these being determined inside the enclosure housing.

SUMMARY

An the object of the present invention is to provide an overvoltagearrester whose working condition and the extent to which it has aged,e.g., temperature, current, gas pressure or gas humidity, can be easilyand conveniently monitored, and a method that allows one to reliablymonitor the arrester and draw conclusions about its condition.

According to the present invention, this object is achieved as follows:A sensor, in particular a temperature sensor in the form of a surfacewave sensor is arranged inside the enclosure housing and integrated intothe arrester block.

A radio-queriable surface wave sensor is a passive, acoustic stripelement to which a query signal in the form of an electromagnetic wavecan be radiated from outside the arrester via an antenna, this signalbeing received via an antenna, radiated back in modified form based oncertain physical values, e.g., the ambient temperature around thesurface wave sensor, and picked up again by an antenna outside theenclosure housing. Thus, the measured value for the measured variable,in particular the temperature inside the enclosure housing of theovervoltage arrester, is made available for further processing to aquery device outside the enclosure housing arranged, for example, at thefoot of the arrester, further measures being unnecessary, and can, forexample, be forwarded to a central data processing station via fiberoptic cable, radio or other measuring line.

Furthermore, the signals radiated back by various different surface wavesensors may be encoded by the individual surface wave sensors, so thatthe signals of closely adjacent overvoltage arresters can easily bedistinguished from one another and assigned accordingly. Moreover, thebehavior of a surface wave sensor may be changed irreversibly if thesensor is temporarily overloaded. Thus, an overload that has occurred inthe past can be determined from the altered behavior of the surface wavesensor. This feature can be used to record arrester overloads or totalfailures.

In normal cases, a discharge current flows for a very short time, sothat a large amount of energy is converted into heat in the arresterblock in a very short time. As a result, for a short time the arresterheats up significantly, which is reflected in a temperature jump thatcan be recorded by the surface wave sensor. The energy converted in thearrester can be calculated from the temperature difference associatedwith a temperature jump of this kind multiplied by the mean heatcapacity of the arrester material and, respectively, from theappropriate calibration curve, and, respectively, the dischargeprocesses can be counted so that the condition of the arrester can bedocumented or maintenance work performed.

To accomplish this, according to the method according to the presentinvention, if the temperature of the arrester block jumps suddenly, theelectrical energy converted in the arrester may be determined from thetemperature difference and the heat capacity.

The temperature values may be recorded on an ongoing basis by thesurface wave sensor. In this case a stationary query unit radiatessignals to the surface wave sensor on an ongoing basis and receives andevaluates the signals that are radiated back.

Alternatively, the individual surface wave sensors of a group ofarresters may be queried using a portable query device only whenmaintenance is required, or periodically.

According to an advantageous embodiment of the overvoltage arresteraccording to the present invention, the surface wave sensor is arrangedinside an at least partly metallic housing, whose walls or othercomponents form an antenna and which is inserted between two dischargeelements in the axial direction of the arrester block, or between adischarge element and a connector electrode.

Typically the metallic housing may be designed as a hollow cylinderhaving caps at both ends, these being made of, for example, aluminum.The metallic housing may then, for example, have at least onelongitudinal slot which extends parallel to the longitudinal axis of thearrester body and functions as a slot antenna for receiving andradiating the signals exchanged between the query device and the surfacewave sensor. To accomplish this, two connecting leads of the surfacewave sensor, which is arranged inside the metallic housing, areconductively connected to this housing.

The metallic housing or a part thereof may also be designed as a patchantenna that includes two conductive layers having a dielectric layerarranged between them. Such slot antennas, patch antennas or micro-stripantennas of this kind are known heretofore according to, for example,Meinke, Grundlach: Taschenbuch der Hochfrequenztechnik (TheHigh-frequency Technology Pocket Handbook), 5th edition, SpringerVerlag, Berlin, Heidelberg, New York, and according to the journalarticle Input Impedance and Radiation Pattern of Cylindrical-Rectangularand Wraparound Microstrip Antennas, IEEE Transactions on Antennas andPropagation, Vol. 38, No. 5, May 1990.

Furthermore, it is useful if the housing conducts the discharge currentif a discharge event occurs.

In this case, the current-carrying capacity of the metallic housing mustbe designed so that the housing can carry the discharge current withoutthe housing or the surface wave sensor being damaged due to overheating.

To this end, the housing may be adhesively bonded to the directlyadjacent discharge elements or held in contact with them by the loadimparted by spring.

According to a further advantageous embodiment of the present invention,the housing is cylinder-shaped and fits into the outline of the arresterblock.

Thanks to this design, high dielectric stability can be achieved, havingno protruding edges that could facilitate discharge.

According to a further useful embodiment of the present invention, thesurface wave sensor is attached to an inside wall of the housing that isdirectly adjacent to a discharge element.

As a result, the surface wave sensor takes on the temperature of theadjacent discharge element with no significant delay, so that thetemperature indicated accurately reflects the instantaneous temperatureof the arrester.

The surface wave sensor may be arranged outside the arrester block, inthe gas area of the overvoltage arrester, so that the temperature of theovervoltage arrester or some other measured variable such as the gasdensity or the gas humidity of the filler gas can be monitored. However,the surface wave sensor must be favorably fitted into the antenna indielectric terms, i.e., so that there is no significant field distortionof the electrical field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the design of an overvoltage arresteraccording to the present invention;

FIG. 2 schematically shows the design of an arrester block having ametallic housing inserted into it;

FIG. 3 schematically shows the design of the metallic housing having thesurface wave sensor;

FIG. 4 schematically shows a housing having a micro-strip antenna;

FIG. 5 schematically shows a housing having a housing wall made up bylayers;

FIG. 6 schematically shows a housing having a partition wall that isdesigned as a slot antenna.

DETAILED DESCRIPTION

Overvoltage arrester 1 for high voltage is mounted on foundation 2. Itincludes, among other things, enclosure housing 3, inside which arresterblock 4 is arranged, a gas-tight seal being formed, sealing armatures 5,6 which seal enclosure housing 3 at both ends, and field controlelements 7, 8. Arrester block 4 includes cylindrical discharge elements15, 16, 17, 18 in the form of non-linear resistors, for example zincoxide resistors, which are held together axially by the load imparted bya spring, or conductively adhesive-bonded, or held together by othermeans. The high-voltage connection is provided at armature 5, while theground is connected to armature 6.

Three elements 11, 12, 13 are shown in black in the arrester block, eachof these representing housing 18 of a surface wave sensor 19. At thefoot of overvoltage arrester 1, query unit 9 is shown, which radiateshigh-frequency electromagnetic waves via an antenna, the wavefrontsbeing shown symbolically as 10. These waves are picked up by theantennas of the surface wave sensors in housings 11, 12, 13 and, afterpassing through the surface wave sensor in question, and after thesignal in question has changed correspondingly based on the measuredvalue detected, e.g., the temperature, are radiated back to query unit9.

Inside query unit 9, the local measured value determined by a givensurface wave sensor, in particular the temperature value, is determinedfrom the signals radiated back and stored. The values can be forwardedto a monitoring station via measuring line 14.

By inserting temperature sensors into arrester block 4, the temperatureof the arrester block can be measured at individual points. If thequiescent current of the arrester increases due to aging, the arrestergradually heats up, and this can be recorded. If it heats up in anon-uniform manner at a given local point, this means specific dischargeelements have aged prematurely.

If a discharge event occurs, a very large amount of electrical energy isconverted to heat in a very short time, and can only be transferredoutwards to enclosure housing 3 via the insulating gas in enclosurehousing 3 in a delayed manner. The short-term temperature jump, whichcan be recorded using the surface wave sensors, provides informationabout the amount of energy converted and thus about the load to whichthe arrester is subject.

In FIG. 2, a detail of a part of arrester block 4 having dischargeelements 15, 16, 17, 18, is schematically shown. Housing 18 of surfacewave sensor 19 is arranged between discharge elements 16, 17. In housing18, longitudinal slot 20 is provided, whose longitudinal directionextends parallel to the axis of arrester block 4. This slot 20 functionsas an antenna for receiving and radiating back the query signals fromquery unit 9.

Housing 18 is made of, for example, aluminum or steel and is sothick-walled that it conducts the discharge current from dischargeelement 16 to discharge element 17 without becoming thermallyoverloaded. Surface wave sensor 19 is conductively connected via itsconnecting leads to two different points on housing 18.

As shown in FIG. 4, may be provided a wraparound patch or patch antennaof any kind on housing 18 or integrated into the outer wall thereofwhich is then conductively connected to surface wave sensor 19 and usedto radiate or receive the signals.

Alternatively, as shown in FIG. 5, at least part of the cylindrical wallof housing 18 may be designed as a body that includes two conductivelayers having a dielectric layer arranged between them, so that thisarrangement can also be used as an antenna.

In this case, inner layer 23 is solid and metallic and carries thedischarge current. Dielectric 24, e.g., PTFE, is applied to this layer,this being covered on the outside by conductive layer 25. The conductivelayer is conductively connected to the solid metallic layer at one end26 of the housing only.

As shown in FIG. 6, partition wall 27 of the housing may be designed asa component thereof in the form of an antenna, e.g., a slot antenna.

The housing may also be designed as a cage that includes electricallyconductive bars that extend parallel to the longitudinal axis of thearrester block.

What is claimed is:
 1. An overvoltage arrester for high or mediumvoltage, comprising: a sealed, gas-tight enclosure housing; an arresterblock arranged inside the housing; and a surface wave sensor arrangedinside the housing and integrated into the arrester block.
 2. Theovervoltage arrester according to claim 1, wherein the surface wavesensor is arranged in an at least partially metallic housing, the atleast partially metallic housing being inserted between a firstdischarge element and a second discharge element.
 3. The overvoltagearrester according to claim 2, wherein the at least partially metallichousing conducts a discharge current when a discharge event occurs. 4.The overvoltage arrester according to claim 2, wherein the at leastpartially metallic housing is cylinder-shaped and fits into an outlineof the arrester block.
 5. The overvoltage arrester according to claim 2,wherein the wave sensor is attached to one of: i) an inside wall, andii) a side wall, of the at least partially metallic housing, the one ofthe inside wall and the side wall being directly adjacent to firstdischarge element.
 6. The overvoltage arrester according to claim 1,wherein the surface wave sensor is arranged in an at least partiallymetallic housing, the at least partially metallic housing being arrangedbetween a first discharge element and a connector electrode.
 7. Theovervoltage arrester according to claim 1, wherein the surface wavesensor is arranged in an at least partially metallic housing.
 8. Theovervoltage arrester according to claim 7, wherein walls of the at leastpartially metallic housing form at least a portion of an antenna.
 9. Amethod for monitoring an overvoltage arrester for high or mediumvoltage, comprising: measuring a temperature inside an enclosure housingof the overvoltage arrester using a surface wave sensor to obtainmeasured values; transmitting the measured values outward via anantenna; and if the temperature of an arrester block of the overvoltagearrester changes suddenly, determining electrical energy converted inthe overvoltage arrester using the temperature change and a heatcapacity.
 10. An overvoltage arrester for high or medium voltage,comprising: a sealed, gas-tight enclosure housing; an arrester blockarranged inside the housing and including at least two dischargeelements; and a surface wave sensor arranged inside the housing andinserted between two of the at least two discharge elements of thearrester block.
 11. The overvoltage arrester according to claim 10,wherein the two of the at last two discharge elements are cylindrical,non-linear resistors.
 12. An overvoltage arrester for high or mediumvoltage, comprising: a sealed, gas-tight enclosure housing; an arresterblock arranged inside the housing; and a surface wave sensor arrangedinside the housing and inserted into the arrester block.